Manganese/oxygen compound with arsenic adsorption

ABSTRACT

A novel technique that is able to efficiently remove, in addition to pentavalent arsenic, trivalent arsenic that has been considered to be difficult to remove. By using a manganese oxygen compound which is characterized by being a product of burning or heating which comprises an oxygen compound of bismuth and an oxygen compound of manganese and by containing manganese as a major component, an aqueous arsenic solution is treated to adsorptively remove the arsenic.

TECHNICAL FIELD

The invention of the present application relates to a manganese oxygencompound with arsenic sorbability, arsenic adsorbent, and a method ofadsorption and removal of arsenic in solution.

BACKGROUND ART

Pollution of rivers and water area such as lakes and marshlands byarsenic is prevailing in Japan and foreign countries, and examples inBangladesh have been widely reported. Soils in this country are abundantin arsenic, and skin failures and diseases by arsenic are often seen ininhabitants in the country using well water polluted with arsenic asdrinking water. While the concentration of arsenic is supposed to reach0.01 to 1 mg/liter (0.01 mg/liter according to the water qualitystandard by WhO) in Nawabganj district where the damage is reported tobe most serious in Bangladesh, no substantial countermeasures are takentoday. On the other hand, pollution by arsenic in Japan is mainly causedby waste water from abandoned mines. The concentration of arsenic in therivers around the mines ascribed to waste water from tunnels afterclosing the mines has been reported to be 0.08 to 1.3 mg/liter, whichexceeds the environmental standard, around Sasagatani Mine in ShimanePrefecture. In the surrounding area of former Horobetu Sulfur Mine inHokkaido, the concentration of arsenic in the river had exceeded farabove the environmental standard before 1975 due to efflux of stronglyacidic water containing a large quantity of arsenic into Benkei River.On the other hand, it was reported that the original arsenicconcentration of 0.2 mg/liter had decreased to about 1/10 of 0.02mg/liter since 1981 thanks to countermeasures to pollution by miningincluding blocking of entrance of tunnels and installation of aneutralization plant for mine water effected by Sobetsu Town. However,the total amount of use of lime cakes, slaked lime and calcium carbonateused for neutralization and removal of arsenic by coprecipitation inthis plant annually accounts for 40,000 to 50,000 tons, and it has beena large problem to ensure landfill sites of a vast amount ofprecipitates generated from the neutralization plant, and to cover theexpense of about 300 million yen per year. There are many waterpollution problems by arsenic such as those ascribed to waste water fromgeothermal power plants and industrial waste other than the problemsabove. However, since the currently prevailing coprecipitation methodinvolves the problems of waste disposal and treatment cost, treatmentsby arsenic adsorbents have been expected as substitutes of the arsenicprocessing method. Particularly, developments of novel adsorbents thatcan directly adsorb trivalent arsenic are considered to be valuable inestablishing an economically advantageous arsenic removal technique,because the process for oxidizing trivalent arsenic into pentavalentarsenic that is relatively easily adsorbed by adding an oxidizing agentmay be omitted.

The object of the present invention for solving the conventionaltechnical problems is to provide a novel technique that is able toefficiently remove, to say nothing of pentavalent arsenic, trivalentarsenic that has been considered to be difficult to remove.

DISCLOSURE OF INVENTION

In order to solve the above problem, firstly, the present inventionprovides a manganese oxygen compound with arsenic sorbabilitycharacterized by being a product of burning or heating which comprisesan oxygen compound of bismuth and an oxygen compound of manganese and bycontaining manganese as a major component.

Further, secondly, the present invention provides the manganese oxygencompound with arsenic sorbability, characterized in that a compound ofmanganese in which a compound of bismuth is added is burned or heated inthe atmosphere or an atmosphere containing oxygen. Further, thirdly, thepresent invention provides a manganese oxygen compound with arsenicsorbability, characterized in that the product of burning or heating isan acid-treated product.

Preferably, fourthly, the present invention provides the manganeseoxygen compound with arsenic sorbability, characterized in that amixture of oxidized bismuth carbonate powder, and manganese carbonatepowder is burned or heated at a temperature of 150° C. to 400° C.Fifthly, the present invention provides the manganese oxygen compoundwith arsenic sorbability, characterized in that a mixture of oxidizedbismuth carbonate and manganese carbonate is in the range of 0.05:1 to1:1.

Sixthly, the present invention provides an arsenic adsorbentcharacterized by comprising the oxygen compound of manganese accordingto any one of the above oxygen compounds of manganese, or a compoundcontaining these oxygen compounds of manganese. Seventhly, the presentinvention provides an arsenic adsorbent characterized by comprising themanganese oxygen compound retained on or filled in a carrier substance.

Further, eighthly, the present invention provides a method of adsorptionand removal of arsenic in solution which comprises, contacting anarsenic adsorbent and an aqueous arsenic solution, and adsorbing andremoving arsenic contained in solution. Further, ninthly, the presentinvention provides a method of reclaiming the arsenic adsorbent whichcomprises, performing an acid treatment to an arsenic adsorbent whichadsorbed arsenic by the above method, making arsenic desorb into an acidsolution, and enabling reclamation of the arsenic adsorbent.

As described above, the oxygen compound mainly containing manganeseaccording to the present invention can solve the problem of loweconomical performance involved in conventional methods (except theadsorption method), while enabling trivalent arsenic, which has beentechnically difficult to efficiently remove by conventional adsorptionmethods, to be efficiently removed by adsorption in a quite short periodof time. For example, the amount of adsorption of trivalent arsenic perone gram reaches 50 mg by using the adsorbent of the present invention.The invention also enables the adsorbent after adsorption of arsenic tobe reclaimed by allowing the adsorbent to contact an acid solution suchas dilute sulfuric acid to readily recover adsorbed arsenic into theacid solution.

It is an important feature of the present invention that the presentinvention is effective not only to arsenous acid as a trivalent arsenicbut also to arsenic acid as a pentavalent arsenic. Since arsenic isusually dissolved in industrial waste water as pentavalent arsenic acidin most cases, the fact that the present invention is effective not onlyto the trivalent arsenous acid but also to the pentavalent arsenic acidmeans that the present invention has a wide applicability in treatingwaste water containing arsenic.

The adsorbent of the present invention exhibits excellent performance asdescribed above while having an advantage that the concentration ofelectrolytes of the aqueous solution as an object of treatment is notrequired to be increased, which is also an advantage of water cleaningusing an adsorbent. In other words, manganese and bismuth as the majorcomponents of the adsorbent are little dissolved in the aqueous arsenicsolution as the object of treatment.

It has been a general method for retaining a powdery adsorbent to fillit in a column after granulation using PVC and the like. However, sincebonding surfaces with PVC are formed in the conventional method, thecontact area between the adsorbent particles and treating solution isreduced to consequently decrease the performance of the column.Accordingly, a novel technique for retaining the powdery adsorbent usingfibrous carrier substances such as ashless pulp or glass wool has beendeveloped in the present invention to improve the drawbacks of theconventional method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the relation between the mixing weight ratioof manganese carbonate and oxidized bismuth carbonate, and the amount ofadsorption of arsenic.

FIG. 2 is a graph showing the relation between the burning temperatureand the amount of adsorption of arsenic.

FIG. 3 is a graph showing the relation after correction of the relationin FIG. 2.

FIG. 4 is a graph showing the relation between initial pH and the amountof adsorption of arsenic.

FIG. 5 is a graph showing the relation between the desorption ratio andadsorption time.

FIG. 6 is a graph showing the relation between the concentration ofarsenic in aqueous solution and the amount of adsorption of arsenic.

FIG. 7 is a graph showing the relation between the stirring time and theconcentration of arsenic.

FIG. 8 illustrates an example of waste water treatment using anadsorption column.

FIG. 9 is a graph showing the result of arsenic waste water treatment bythe adsorption column method.

FIG. 10 illustrates an example of a simplified water cleaning methodusing an adsorption mat.

FIG. 11 illustrates an example of a portable water cleaning method usingan adsorption pack.

FIG. 12 is a graph showing the result of waste water treatment by anadsorption pack method.

FIG. 13 is a graph showing the result of treatment of pentavalentarsenic containing waste water.

BEST MODE FOR CARRYING OUT THE INVENTION

While the invention is featured as described above, embodiments thereofwill be described hereinafter.

The oxide compound of manganese provided by the invention has an arsenicsorbability as its function. The compound contains an oxygen compound ofbismuth (Bi) and an oxygen compound of manganese (Mn) with manganese asits major component.

This product of burning or heating refers to as a heated product, andmeans that the product is heated either by the heat of a chemicalreaction induced by mixing base materials, by drying, or by a heattreatment accompanied by a chemical reaction. Burning, or heating isusually carried out at 100° C. or more, preferably in the temperaturerange of 150 to 500° C., and the oxygen compound of bismuth and theoxygen compound of manganese are involved by heating. The “oxygencompound” is, as well, defined as an oxide or an oxide as a complexoxygen compound, or a compound mainly comprising the oxygen compound andhaving oxygen containing groups such as carboxylate groups.

Various bismuth compounds and manganese compounds may be used as thebase materials for forming the oxygen compound in the atmosphere or anatmosphere containing oxygen in burning or heating. The base materialmay be carboxylate, nitride, sulfate, organic acid salts and halides,and favorably used compounds are solids or powders. The material may beformed by precipitation by a sol-gel method.

In a representative example, oxidized bismuth carbonate powder andmanganese carbonate powder are mixed, and the mixed powder or a moldedbody thereof is burned in the temperature range of 150 to 400° C.,preferably 170 to 250° C. The mixing ratio of the base materials such asoxidized bismuth carbonate and manganese carbonate in the representativeexample is preferably 0.01:1 to 1:1 in the molar ratio of bismuth tomanganese considering the arsenic adsorbing ability.

It is effective to activate the burned product by an acid treatment forpreparing the arsenic adsorbent. Dilute nitric acid, sulfuric acid,hydrochloric acid and the like may be used for the acid treatment.

The arsenic adsorbent of the present invention may be retained on orfilled in a carrier substance such as ashless pulp and glass wool foruse in removal of arsenic in aqueous solution by adsorption.

Trivalent arsenic has been treated after converting it into readilytreatable pentavalent arsenic by adding an oxidizing agent in theconventional art. However, it is a problem that water quality isdeteriorated by increasing the electrolyte concentration in water whilebeing low in cost performance. Accordingly, developments of adsorbentscapable of directly treating trivalent arsenic in water have beendesired. The present invention can realize a high performance,economically advantageous adsorption treatment of trivalent arsenic aswell as pentavalent arsenic by the steps comprising burning themanganese compound by adding a small amount of a bismuth compound, andapplying the obtained metal oxide containing manganese as a majorcomponent with a small amount of bismuth to waste water containingarsenic, desirably after an acid treatment. Adsorption of trivalentarsenic has been experimentally proved as arsenic in arsenous acid(HAsO₂) by measuring pH and redox potential of the aqueous arsenicsolution.

A retention layer of the powdery adsorbent excellent in chemicalresistance in repeated uses of the column may be obtained by using glasswool and the like as the carrier of the adsorbent. Incineration fordisposal of the column in an incinerator after repeated uses of thecolumn is possible by using ashless pulp as the carrier of theadsorbent. The ashless pulp accounting for the greater part of thevolume of the retaining layer involving the powdery adsorbent is almostcompletely burnt up, and the residue only comprises the component of theadsorbent after incineration.

Accordingly, the present invention provides a novel adsorbent capable ofefficiently adsorbing, to say nothing of pentavalent arsenic, trivalentarsenic that has been considered to be difficult to remove from anaqueous solution by the conventional art. The adsorbent has a highperformance in which the maximum amount of arsenic per 1 g of theadsorbent reaches 50 mg or more.

The following procedure gives a largest effect in applying the adsorbentof the invention to an aqueous arsenic solution. This will be madeapparent in the examples to be described hereinafter.

(a) Manganese carbonate powder (MnCO₃, reagent special grade) andoxidized bismuth carbonate powder (Bi₂(CO₃)O₂, reagent special grade)are mixed in a weight ratio of 1:0.1 to 1:0.2. A metal oxide containingbismuth and mainly containing manganese is synthesized by burning themixture at 200° C. for 4 hours and 30 minutes using an electric furnace.

(b) The metal oxide containing bismuth and mainly containing manganeseobtained in (a) is suspended in dilute nitric acid with a concentrationof about 0.5 mol/liter to remove remaining carbonate components byvaporization. Then, the metal oxide is washed with pure water to removeadhered nitric acid.

(c) The sample obtained in (b) is dried at about 100° C. for 1 hourusing a drying machine. The adsorbent is produced by the procedureabove.

(d) The adsorbent is suspended in dilute nitric acid with aconcentration of about 0.5 mol/liter followed by stirring for 30 minutesto 1 hour, filtered, washed with pure water, and suspended again in anaqueous arsenic solution for use as the adsorbent.

(e) After the concentration of arsenic in the aqueous arsenic solutionhas decreased to 0.1 mg/liter as a standard of waste water, theadsorbent is retrieved from the aqueous arsenic solution by, forexample, filtration. Purified waste water becomes possible to dischargeinto a public water area.

(f) Adsorbed arsenic is desorbed and concentrated in dilute sulfuricacid by adding a small volume of dilute sulfuric acid with aconcentration of 0.5 mol/liter or less to the adsorbent after adsorbingretrieved arsenic, followed by stirring for about 30 minutes.

(g) Since adsorption ability of the adsorbent after desorption ofarsenic is recovered again, the adsorbent is used again by allowing itto contact the aqueous arsenic solution.

While the adsorbent is suspended in the aqueous arsenic solution as apowdery adsorbent in the example above, the adsorbent may be granulatedor retained on a porous carrier, if necessary, to fill in a column forindustrial applications in order to remove arsenic by passing theaqueous arsenic solution through the column.

While the invention will be described in more detail with reference tothe examples, the invention is by no means restricted to the examples.

EXAMPLES Example 1 Synthesis of Adsorbent and Adsorption of Arsenic

(Synthesis of Adsorbent)

Manganese carbonate powder (MnCO₃, reagent special grade) and oxidizedbismuth carbonate powder (Bi₂(CO₃)O₂, reagent special grade) werethoroughly mixed by changing the mixing ratios to several steps. About20 g of each mixed powder was transferred to a ceramic crucible, and wasburned at 400° C. for 4.5 hours using an electric furnace, followed bycooling to room temperature by allowing the crucible to stand still. Themetal oxide obtained containing a small amount of bismuth and manganeseas a major component after burning is used as an adsorbent for thearsenic adsorption experiment. The optimum mixing weight ratio betweenmanganese carbonate (MnCO₃) powder and oxidized bismuth carbonate(Bi₂(CO₃)O₂) powder was determined for obtaining the highest amount ofadsorption. The effect of adding bismuth was confirmed by comparing theadsorptive performance of manganese oxide, which was obtained by burningonly manganese carbonate (MnCO₃) powder without mixing with oxidizedbismuth carbonate (Bi₂(CO₃)O₂) powder, with the adsorptive performanceof the adsorbent above.

Then, the sample was heated or burned by changing the temperatures to150° C., 200° C., 250° C. and 300° C. for 4.5 hours followed by allowingthe samples to cool to room temperature. The optimum burning temperaturewas investigated by arsenic adsorption experiments using each metaloxide obtained containing a small amount of bismuth and mainlycontaining manganese as the adsorbent.

(Experimental Method of Arsenic Adsorption)

An aqueous arsenic standard solution (made by Wako Pure ChemicalIndustries, Ltd.) containing a total concentration of trivalent arsenicof 1000 mg/liter prepared from a reagent (As₂O₃) was diluted withion-exchange water to prepare 1000 ml each of arsenic solutions withconcentrations of 10 mg/liter, 20 mg/liter or 40 mg/liter, and thesolution was used for each experiment. The pH values of the arsenicsolutions were adjusted using an aqueous sodium hydroxide solution.Subsequently, 1.0 g of the adsorbent obtained by each experiment abovewas weighed with an electronic balance, and was suspended in 1000 ml of0.5 mol/liter of diluted nitric acid (may be diluted sulfuric acid orhydrochloric acid) followed by stirring for 1 hour. After stirring, thesuspension was filtered with suction using a glass fiber filtrationpaper (GS25, made by Toyo Roshi Kaisha, Ltd.) with a pore size of 0.6mm, followed by washing by allowing 1000 ml of ion-exchange water toflow through (this process is called as an acid treatment hereinafter)The activated adsorbent obtained by the acid treatment was suspended inan arsenic aqueous solution followed by stirring for 1 hour. Twentymilliliters each of the aqueous arsenic solutions were sampled at 5, 10,20, 30 and 60 minutes after the start of stirring. A disposable membranefilter (DISMIC-25 made by Toyo Roshi Kaisha, Ltd.) with a pore size of0.2 μm was used for filtration. The concentration of arsenic in eachfiltered sample was measured with an ICP atomic emission analyzer(ICPS-1000III made by Shimadzu Corporation) to obtain time dependentchanges of the arsenic concentration in the aqueous arsenic solution.

(Amount of Adsorption of Arsenic and Mixing Ratio of Base Material)

For synthesizing the arsenic adsorbent, the mixing ratio of manganesecarbonate powder (MnCO₃, reagent special grade) and oxidized bismuthcarbonate powder (Bi₂(CO₃)O₂, reagent special grade) were changed asdescribed above to investigate the optimum mixing ratio. The burningtemperature was 400° C., and the results are shown in FIG. 1. FIG. 1shows that the optimum mixing ratio for obtaining the highest amount ofadsorption is MnCO₃ :Bi₂(CO₃)O₂ of about 1:0.1 to 1:0.2 in the mixingweight ratio. On the contrary, the amount of adsorption was extremelydecreased in the manganese oxide containing no bismuth added (mixingratio 1:0) as compared with the oxide in which bismuth is added,indicating that the arsenic adsorption performance is improved by addingbismuth.

Peaks of bismuth oxide and oxidized bismuth carbonate, as well as abroad peak at 2θof 37° a scribed to amorphous manganese oxide, wereobserved by confirmation with the X-ray diffraction pattern in theproducts of burning with the mixing ratio in the range of 1:0.1 to1:0.2.

(Amount of Adsorption of Arsenic and Burning or Heating Temperature)

In the synthesis of the arsenic adsorbent, the change of the amount ofadsorbed arsenic to the difference of the temperature was investigatedwhen a mixed powder of manganese carbonate and oxidized bismuthcarbonate was heated using an electrical furnace. The results are shownin FIG. 2. FIG. 2 shows that a high amount of adsorption is obtainedwhen the temperature is about 300° C. However, it was found that theweight of the adsorbent was decreased to about one half of the initialweight of 1 g, when the adsorbent suspended in an aqueous arsenicsolution was filtered and weighed after completing the adsorptionprocedure. This decrease of the weight of the adsorbent is supposed tobe ascribed to the fact that manganese carbonate as a base reagentmaterial is left behind in the adsorbent obtained after burning orheating, and carbonates are lost by vaporization when the adsorbent istreated with an acid. It was made clear that the adsorbent obtained byburning or heating at 200° C. shows the highest amount of adsorption asshown in FIG. 3, by correcting the results in FIG. 2 considering theweight loss as described above.

(Amount of Adsorption of Arsenic and pH)

The effect of pH of the aqueous solution of the removal object on theamount of adsorption of arsenic was investigated. The result showed thatgood adsorption of arsenic is attained when pH of the aqueous arsenicsolution is weakly acidic. Accordingly, arsenic is considered to beefficiently removed by previously adjusting pH of the aqueous arsenicsolution as the object of removal.

(Desorption of Arsenic from the Adsorbent)

Arsenic adsorbed on the adsorbent is efficiently desorbed by allowingthe adsorbent to contact an acid such as dilute sulfuric acid. Therelation between the kind of the acid solution used for desorption anddesorption ratio is shown in FIG. 5. FIG. 5 shows that a high degree ofdesorption is possible by using dilute hydrochloric acid or dilutesulfuric acid.

(Concentration of Arsenic in Aqueous Solution and Amount of Adsorptionof Arsenic)

The effect of the concentration of arsenic in the aqueous solution onthe amount of adsorption is shown in FIG. 6. FIG. 6 shows that theamount of adsorption increases as the concentration of arsenic isincreased.

(Practical Application to Aqueous Waste Arsenic Solution)

Effectiveness of the synthesized adsorbent to practical aqueous wastearsenic solution containing trivalent arsenic was confirmed. The objectof treatment was waste water from a currently operating geothermal powerplant. This waste water contains arsenic in a concentration of 3.5mg/liter. The component and pH of this waste water are shown in Table 1.Table. 1 shows that this waste water contains many components other thanarsenic. In an actual experiment, 1 g of the adsorbent having the mixingratio of 1:0.2 as described above and burned at 200° C. was treated withan aqueous nitric acid with a concentration of 0.5 mol/liter, and theadsorbent was suspended in 1 liter of waste water with stirring for 1hour. The results are shown in FIG. 7. FIG. 7 shows that theconcentration of arsenic in the waste water was decreased to 0.1mg/liter or less that is the standard of waste water in a period of asshort as 5 minutes from the initial concentration of 3.5 mg/liter. Thisresults shown that the adsorbent of the invention is quite effective forthe practical arsenic waste water.

TABLE 1 Components of practical waste water and pH ChemicalConcentration Element (mg/l) Na 1790 K 257 Ca 28.0 Mg 0.70 Cl 2980 SO₄144 HCO₃ 23.9 Fe 4.5 HBO₃ 159 As 3.50 T-SiO₂ 667 Li 10.8 pH 7.0

Example 2 [Retention and Adsorption of Powdery Adsorbent using AshlessPulp and Glass Wool]

The adsorbent is granulated or retained on a porous carrier to fill in acolumn, if necessary, for industrial applications, and arsenic isremoved by allowing an aqueous arsenic solution to flow through thecolumn.

(1) Method for retaining powdery adsorbent

An appropriate amount of ashless pulp or glass wool with a thickness ofabout 1 μm was added in pure water with thorough stirring. The diameterof the ashless pulp or glass wool depends on the size of the adsorbentparticles to be retained. For example, the diameter of the adsorbentparticles as the retention object is 1 to several tens microns. Then,the adsorbent is added to the suspension of ashless pulp or glass woolwith additional stirring. An inorganic acid such as hydrochloric acid ornitric acid is added when necessary depending on the property of theadhesive with stirring for a predetermined time. Adding the inorganicacid with stirring activates the surface of the adsorbent particles.

The suspension is added in small portions from the top of a cylinder forpreparing an adsorption column when glass wool is used, and the liquidis completely discharged from the bottom of the column with suctionusing a pump every time for adding the suspension. This procedure isrepeated until a desired thickness is obtained to form a retention layerin which the powdery adsorbent is embedded in the glass wool fiber.

When ashless pulp is used, on the other hand, the suspension is pouredinto the cylinder for preparing an adsorption column from the top of thecolumn. The suspension is stirred with a bar so that the pulp andadsorbent are uniformly precipitated in the column while allowing theliquid to be gradually discharged from the bottom of the column, and aretention layer is formed so that the powdery adsorbent is embedded inthe ashless pulp fibers.

(2) Examples Depending on the Retention Method

Examples of treatments of water containing arsenic by applying theretention methods of the invention described above are explained below.

(a) Adsorption Column Method

In this method, wastewater containing trivalent arsenic discharged fromsemiconductor factories is the object of treatment. As shown in FIG. 8,arsenic is removed by injecting wastewater with compression into thecolumn from an waste water tank using a pump. A large volume ofwastewater may be continuously processed by this method. A valve isprovided between the pump and adsorption column to control the feed rateto the adsorption column. The adsorption column is hermetically sealedto prevent the arsenic adsorbent from contacting the air in order toprotect the adsorptive performance of the adsorption column from beingdeteriorated due to drying of the adsorbent. FIG. 9 shows theexperimental results of arsenic wastewater by this method. The resultswere obtained from experiments by flowing an aqueous arsenic solutionwith an arsenic concentration of 1 ppm through a cylindrical adsorptioncolumn with a diameter of 2 cm and a length of 10 cm at a flow speed of300 ml/h.

(b) Adsorption Mat Method

This method has been devised as an water cleaning technology fortreating serious contamination of drinking water with arsenic occurringin Bangladesh, which is expected as a simple water cleaning method thatdoes not require any electricity at all. The treatment tank shown inFIG. 10 comprises an outer frame equipped with an water tap, an arsenicadsorption mat, and charcoal, sand and gravel that has been used fordomestic filtration tank. This device is featured in that the structureis simple and hardly broken, and cleaning of water from arsenic ispossible by only supplying the outer frame and adsorption mat to theinstallation site. The gravel layer and sand layer remove suspended fineparticles in water, the charcoal layer removes organic substances, andthe adsorption mat to enable safe drinking water to be easily obtainedremoves arsenic. In addition, the structural feature of the method isthat the elevation of the water tap is made to be higher than theinstallation position of the arsenic adsorption mat so that theadsorption mat is always soaked in water. This enables the adsorbent tobe protected from being dried by contacting the air to consequentlyprevent the performance of the adsorption mat from being deteriorated.

An arsenic adsorbent previously activated with an inorganic acid isretained on the adsorption mat. The adsorption mat should behermetically sealed to the air in a sufficiently moist state, and isstored separately from the outer frame. The adsorption mat istransported to the installation site of the device in a hermeticallysealed state with a film. The film is peeled immediately before use andis laid in the outer frame, and sand, gravel and charcoal are filledthereon as shown in the drawing.

(c) Adsorption Bag Method

This method was devised as a portable cleaning method of water fromarsenic for the purpose of enhancing simplicity and convenience ascompared with the method (b). The method is illustrated in FIG. 11. Asmall amount of glass wool for obtaining good water permeability orfiber of ashless pulp or the like, and the arsenic adsorbent are sealedin an adsorption bag. The bag is placed in water to be treated, andarsenic is removed by adsorption by stirring water to be treated.

The arsenic adsorbent in the adsorption bag is previously activated withan inorganic acid, and the bag is hermetically sealed in a plastic bagin a moist state. The adsorptive ability of the arsenic adsorbent issustained for a long period of time by hermetic sealing. Taking theadsorption bag out of the plastic bag by breaking the plastic bag mayinstantaneously use the adsorbent. FIG. 12 shows the results of use ofthis method. FIG. 12 shows the decrease of the concentration of arsenicafter placing one adsorption bag with stirring in 1 liter of watercontaining trivalent arsenic.

Example 3 [Removal of Arsenic (Pentavalent Arsenic) from IndustrialWastewater]

(Experimental Wastewater)

Arsenic (V) was removed from practical industrial waste water having thecompositions shown in Table 2 using an adsorbent having a mixing weightratio of 1:0.2 as described previously and burned at 200° C. The arsenicconcentration of waste water was 0.028 mg/liter, which exceeds theenvironmental standard of 0.01 mg/liter. Arsenic in this wastewater wasconfirmed to be arsenic acid from the measurement of the redoxpotential.

TABLE 2 concentration component (mg/l) As 0.028 Mo 310 V 2.5 Pb 0.3 Cd0.1 Cr 0.1 Se 0.3 Mn 3.4 Zn 0.1 Cu 0.1 P 1.0 Fe 0.1 Al 1.3 NH₄—N 1980NO₃—N 850 Na 3720 Mg 6800 Ca 140 S 9495 Cl 6750 pH 7.8(Experimental Conditions)

The adsorbent (1.44 g) after an acid treatment with 0.5N nitric acid wassuspended in 1 liter of experimental waste water. Samples ofexperimental waste water were sampled by filtration at every time lapseof 5, 15, 30, 60 and 120 minutes after suspending the adsorbent. Thechanges of arsenide concentration in experimental waste water wereinvestigated using an ICP atomic emission analyzer equipped with ahydride compound generator, which is a higher analytical sensitivitythan conventional ICP atomic emission analyzer.

(Experimental Results)

As shown in FIG. 13, the concentration of arsenic was decreased with thetime lapse of stirring as indicated in the vertical axis, and reached toa level below the environmental standard of 0.01 mg/liter 30 minutesafter suspending the adsorbent. It was confirmed that the adsorbent ofthe invention is also effective for removing arsenic (V) in practicalindustrial waste water in which various other components exist togetheras shown in Table 2.

Example 4 [Removal of Arsenic from Artificial Arsenic (V) Waste Water]

(Experimental Waste Water)

Artificial waste water (3 liters) of arsenic (V) was prepared bydissolving a reagent (Na₂HAsO₄) in pure water. The concentration ofarsenic was 10 mg/liter, and the solution was adjusted to pH 7 by addingan aqueous sodium hydroxide solution.

(Experimental Conditions)

After treating 1 g of the adsorbent in Example 3 with 0.5N nitric acidfor 30 minutes, the adsorbent was washed with pure water, and suspendedin experimental waste water with stirring for 1 hour.

(Experimental Results)

The concentration of arsenic in experimental waste water after a timelapse of 1 hour was determined with an ICP atomic emission analyzer, andwas found to be decreased to7.2 mg/liter. The weight of the adsorbentrecovered from experimental waste water by filtration was 0.5 g. Theamount of adsorption of arsenic (V) per unit weight of the adsorbent wascalculated to be 16.8 mg/g. The value was almost comparable to theexperimental result obtained by using an artificial arsenic waste watercontaining arsenic (III) prepared using a reagent As₂O₃, showing thatthe adsorbent of the invention is an effective adsorbent for trivalentarsenic as well as for pentavalent arsenic.

INDUSTRIAL APPLICABILITY

As hitherto described in detail, the present invention provides a newtechnology that enables pentavalent arsenic as well as trivalent arsenicthat has been considered to be difficult to remove to be efficientlyremoved from waste water.

1. A manganese oxygen compound with pentavalent or trivalent arsenicsorbability which is a product of burning or heating which consists ofan oxygen compound of bismuth and an oxygen compound of manganese andcontains manganese as a major component, wherein the molar mixing ratioof the compound of bismuth and the compound of manganese is in the rangeof 0.01:1 to 1:1.
 2. The manganese oxygen compound with pentavalent ortrivalent arsenic sorbability according to claim 1, wherein a compoundof manganese in which a compound of bismuth is added is burned or heatedin the atmosphere or an atmosphere containing oxygen.
 3. The manganeseoxygen compound with pentavalent or trivalent arsenic sorbabilityaccording to claim 1, wherein a mixture of oxidized bismuth carbonatepowder and manganese carbonate powder is burned or heated at atemperature of 150° C. to 400° C.
 4. An arsenic adsorbent comprising theoxygen compound of manganese according to claim 1, or a compoundcontaining the oxygen compound of manganese.
 5. A method of adsorptionand removal of arsenic in solution which comprises, contacting anarsenic adsorbent according to claim 4 and an aqueous arsenic solution,and adsorbing and removing arsenic contained in solution.
 6. A method ofreclaiming the arsenic adsorbent of claim 5 which comprises, performingan acid treatment on the arsenic adsorbent which adsorbed arsenic,making arsenic desorb into an acid solution, and recovering the arsenicadsorbent.
 7. An arsenic adsorbent comprising the manganese oxygencompound according to claim 1 retained on or filled in a carriersubstance.
 8. A method of adsorption and removal of arsenic in solutionwhich comprises, contacting an arsenic adsorbent according to claim 7and an aqueous arsenic solution, and adsorbing and removing arseniccontained in solution.
 9. A method of reclaiming the arsenic adsorbentof claim 8 which comprises, performing an acid treatment on the arsenicadsorbent which adsorbed arsenic, making arsenic desorb into an acidsolution, and recovering the arsenic adsorbent.
 10. A process forproducing the manganese oxygen compound with pentavalent or trivalentarsenic sorbability according to claim 1, which comprises mixing a basematerial for the oxygen compound of bismuth and a base material for theoxygen compound of manganese for forming the manganese oxygen compound,and burning or heating the base materials.
 11. The process according toclaim 10, wherein the base materials are burned or heated at atemperature of 150°C. to 400°C.
 12. The process according to claim 10,which further comprises treating the product of burning or heating withan acid.
 13. The manganese oxygen compound with pentavalent or trivalentarsenic sorbability according to claim 1, wherein the product of burningor heating is an acid-treated product.